JPH1068479A - Bonding type lap joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve bonding strength by locally increasing the bending rigidity of a member to be bonded only in a part in the vicinity of a bonding part in a lap joint in which two members are bonded to each other with an adhesive. SOLUTION: In a joint in which two members 7, 8 are lapped and bonded to each other, the bending rigidity of the members 7, 8 is locally increased only in a part in the vicinity of a bonded part. When the members 7, 8 are lapped and bonded to each other, a strap 9 is manufactured from the material of relatively large bending rigidity, and the strap 9 is bonded in the vicinity of the bonded part of the members 7, 8. Means to locally increase the bending rigidity of the bonded part include methods in which only the part to be bonded is made of the material of large bending rigidity, and the thickness of only the part to be bonded is increased. Such lap joints are preferably used for the part to be bonded in a body frame member or a flange part of a panel, a weld bonding junction part, an assembly part of a side structure of a rolling stock, and a connection part of the side structure to a roof or a truck.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lap adhesive joint in which two members are bonded with an adhesive, and more particularly, to a lap adhesive joint in which the strength of an adhesive portion is improved.

[0002]

2. Description of the Related Art Destruction of an adhesive portion in an adhesive joint is variously classified depending on the form of the joint. The fracture at the adhesive interface, the cohesive failure which is the destruction of the adhesive itself, or It can be classified into any of composite fracture of interfacial fracture and cohesive fracture. The bond distribution is closely related to the stress distribution of the bonded portion. Generally, simple lap joints are under tensile load (P)
1, the transmission of the force from the adherend 1a to the adherend 1b shown in FIG.
Is maximized at the end of the adhesive layer 2 and is represented by a hyperbolic function. As described above, the destruction of the bonding portion is caused by the destruction occurring from the end of the bonding layer 2.
The destruction progresses into the interior of the device, leading to eventual destruction. The state of this destruction is schematically shown in FIG.

In view of the results of the above study, it is considered that the key to the measures against destruction is the stress distribution at the end of the bonded portion. For this purpose, various measures have conventionally been taken, but these measures can be broadly classified into two: "improvement of the shape of the bonded portion" and "improvement of the physical properties of the adhesive". The above-described method is a method of reducing the concentration of stress by applying various measures to the shape of the bonded portion in order to avoid concentration of stress at the end of the bonded portion. According to the method, the stress distribution generated in the adhesive layer depends on the longitudinal elastic modulus (Young's modulus) of the adhesive, and the stress concentration on the end portion of the bonding portion tends to decrease as the Young's modulus of the adhesive decreases. It is a method that utilizes that. Hereinafter, these methods will be described in detail.

[0004] Improving the shape of the bonded portion a. A method of tapering the lap end of the adherend
As shown in FIG. 2 (a), the fracture strength of the lap adhesive joint where the lap end is tapered 3 to make the end of the adhesive layer thinner is shown in FIG. 2 (b). It is reported that the value is improved about twice as compared with the value of the simple lap adhesive joint shown. FIG. 3 is a view showing this, in which the taper at the wrap end (line 4 in FIG. 3) is twice as large as the taper at the wrap end (line 5 in FIG. 3). It can be seen that the breaking strength (F) is improved to some extent.

B. A method of causing the adhesive to protrude from the end (hereinafter, referred to as “conventional bonding method 2”) As shown in FIG. 4, analysis of a simple overlapped adhesive joint in which the adhesive protrudes from the end and a spew fillet 6 is provided. It has been reported that the provision of the fillet 6 reduces the maximum shear stress by 30%, and is effective in reducing stress concentration.

Concerning improvement of physical properties of adhesive a. A method using an adhesive having a small longitudinal modulus (Young's modulus) (hereinafter referred to as “conventional bonding method 3”) For a simple lap joint in which stainless steel is bonded with an epoxy-based adhesive, the Young's modulus of the adhesive and the bonded portion As a result of examining the relationship with the stress distribution that occurs, when using an adhesive with a low Young's modulus at the end of the adhesive layer, the stress concentration at the end of the adhesive layer is alleviated than using an adhesive with a high Young's modulus alone Has been reported.

However, each of the above bonding methods has the following disadvantages. That is, the conventional bonding method 1 requires special machining to form a taper, and when the material is a thin plate or when applied to a composite material such as FRP, the tapering itself is difficult.

Further, in the conventional bonding method 2, in order to stabilize the bonding strength and obtain reproducibility, it is necessary to machine the protruding portion of the adhesive. Further, since the adhesive is exposed, the amount of protrusion may decrease with time depending on the use environment, and the strength may be reduced. further,
There is a limit to the amount of protrusion, and no significant improvement in strength can be expected. In addition, the appearance of the bonded portion is not good.

The conventional bonding method 3 does not require machining of the adherend, but takes into consideration not only strength but also other properties (heat resistance, corrosion resistance, workability, economy, etc.) in selecting an adhesive. It is necessary to use an adhesive having a low Young's modulus unnecessarily. In addition, the range of the Young's modulus of the adhesive is also limited, and a great improvement in strength cannot be expected.

[0010] As described above, the conventional bonding methods 1 to 3 have drawbacks such as the necessity of special processing for that purpose and the inability to expect a great improvement in strength.

Therefore, the present inventor studied factors affecting the shear stress distribution of the bonded portion in order to improve the strength of the bonded portion. These factors include "Lap length (overlap length)", "Thickness of adherend", "Thickness of adhesive layer", "Type of adhesive", "Young modulus of adherend", etc. Assuming that "wrap length", "adhesive layer thickness" and "adhesive type" are the same, "substrate thickness" and "substrate Young's modulus" The influence as shown in FIGS. 5 and 6 was analyzed. FIG. 5 shows a board width of 25 mm.
When the SS400 with a length of 150 mm is overlapped with each other with a wrap length of 25 mm and adhered, and one end is fixed and the other end is pulled at 4.2 kN, "distance from the bonded end (d) / lap length" 2 shows the effect of the thickness (t) of the adherend on the relationship between the thickness and the “shear stress”. As shown in FIG. 5, when the thickness (t) of the adherend increases, the maximum shear stress decreases, and the distribution of the shear stress flattens. FIG. 6 shows SS400s having a thickness of 5 mm, a width of 25 mm and a length of 150 mm, or FRs.
P (fiber reinforced plastic) is overlapped with a wrap length of 25 mm and adhered, one end is fixed, and the other end is 4.2 kN.
The relationship between "distance (d) from the bonded end / lap length" and "shear stress" when pulling is shown. As shown in FIG. 6, the maximum shear stress of the material having a high Young's modulus (SS400) is lower than that of the material having a lower Young's modulus (FRP), and the distribution of the shear stress is flattened.

According to the above analysis results, when the thickness of the adherend is increased or the Young's modulus of the adherend is increased, the maximum shear stress generated in the bonded portion is reduced, and the distribution of the shear stress becomes flat. Then, it was considered that the bonding strength could be improved. Next, the effect on the bonding strength when the thickness and Young's modulus of the adherend were actually changed was investigated. FIG.
SS400 when SS400 with a board width of 25 mm and a length of 150 mm are overlapped and bonded with a wrap length of 25 mm
Shows the relationship between the sheet thickness and the adhesive strength (tensile load P / sheet width W), and it is clear that the adhesive strength improves as the sheet thickness increases. FIG. 8 shows a plate thickness of 5 mm, a plate width of 25 mm and a length of 15 mm.
The relationship between the Young's modulus and the adhesive strength when a 0 mm adherend is overlapped with a wrap length of 25 mm is shown, and it is clear that the adhesive strength increases as the Young's modulus increases. Increasing the thickness and Young's modulus of the adherend is equivalent to increasing the bending stiffness, and the relationship shown in FIGS. 7 and 8 in which the relationship shown in FIG. It is. When the bending stiffness is increased, the distribution of the shear stress generated in the bonding portion becomes uniform, and the stress concentration at the edge of the bonding layer is reduced. As a result, the bonding strength seems to increase as shown in FIG. It is.

However, in practice, it is uneconomical to increase the plate rigidity and the Young's modulus throughout the adherend to increase the bending rigidity in order to improve the adhesive strength.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a lap adhesive joint capable of improving the strength of an adhesive portion by a simple means. It is in.

[0015]

In order to achieve the above object, according to the present invention, the bonding strength can be improved by locally increasing the bending rigidity of the adherend only in the vicinity of the bonding portion.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, the present invention is characterized in that in a lap adhesive joint in which two members are superposed and bonded, the bending rigidity of the two members to be bonded is locally increased only in the vicinity of the bonded portion. A lap adhesive joint is defined as a first invention, and in the first invention, a lap adhesive joint in which a means for locally increasing the bending stiffness near an adhesive portion is a second plate is defined as a second invention.

According to the present invention configured as described above,
As shown in FIG. 10, when the member 7 and the member 8 are overlapped and bonded to each other, the contact plate 9 is bonded to the bonding portion of the members 7 and 8, and the bending rigidity near the bonding portion is locally increased. In addition, the distribution of shear stress can be made uniform, and the concentration of stress at the end of the adhesive layer can be reduced.

[0018]

Embodiments of the present invention will be described below. As shown in FIG. 10, when the member 7 and the member 8 are overlapped and bonded, the contact plate 9 is made of a material having relatively high bending rigidity (metal or the like), and the vicinity of the bonded portion between the members 7 and 8 is formed. The plate 9 is adhered. Since it is an adhesive, it can be used regardless of the material of the members 7 and 8. Since a direct load is not applied to the contact plate 9 and a large adhesive strength is not required between the contact plate 9 and the members 7 and 8,
The bonding work of the plate is simple.

FIG. 11 shows a plate having a thickness of 3 mm, a width of 25 mm and a length of 1 mm.
When 50mm SS400s are overlapped with each other with a wrap length of 25mm and bonded together, the thickness is 2mm, the width is 25mm and the length is 50mm
When the center of the contact plate S is 35 mm from the end of SS400, one end is fixed and the other end is pulled at 4.2 kN, the distance from the adhesive end (d)
2 shows the results of analysis of the relationship between “/ lap length” and “shear stress”. As shown in FIG.
The maximum shear stress is lower than that of "without plate",
The distribution of shear stress is flattened.

FIG. 12 shows a sheet thickness of 5 mm, a sheet width of 25 mm and a length of 1 mm.
When 50 mm FRPs are overlapped with each other with a lap length of 25 mm and bonded, when the center of the plate S having a plate thickness of 2 mm and a plate width of 25 mm is located 35 mm from the end of the FRP, the length of the plate S It is a figure which shows the change of the adhesive strength when changing it to 25 mm, 50 mm, and 75 mm, and "the thing with this plate (●)"
In each case, the adhesive strength was higher than that of “without this plate (dotted line)”. However, the length of this plate is 25mm and 50
The bond strength of the mm-type one does not change. Comparing this relationship with the horizontal lap allowance of the upper and lower plates, the center position of the upper and lower plates is 45 mm apart in the horizontal direction, so the upper and lower plates have a length of 25 mm, 50 mm, and 75 mm. The horizontal lap of the board is “none”, “5mm”, “30”, respectively.
mm]. That is, if the horizontal lap allowance of the upper and lower contact plates is increased to a certain value or more, it is considered that the bending rigidity of the bonding portion is further increased and the bonding strength is further increased.

FIG. 13 shows a sheet thickness of 5 mm, a sheet width of 25 mm and a length of 1 mm.
When 50 mm FRPs are overlapped and bonded with a wrap length of 25 mm, the center of the plate S bonded to one FRP is set to the center of the other FRP for the plate S having a thickness of 2 mm, a width of 25 mm and a length of 50 mm. The change in adhesive strength when the distance X is changed in the horizontal direction from the end is shown. When the distance X is “zero”, the adhesive strength is maximum. The distance X is “zero” when the horizontal wrap margin of the pressing plates adhered to both FRPs is 25 mm. As the distance X increases, the pressing plates S and S are separated from each other in the left and right direction. It is considered that the lap margin in the direction is shortened (or the lap margin is eliminated), and the adhesive strength is reduced.

As means for locally increasing the bending stiffness of the bonding portion, as described above, there are the following methods in addition to the method of bonding the plate to the vicinity of the bonding portion.

Only the bonding portion is made of a material having high bending rigidity. As shown in FIG. 14, only the bonding portion between the two members 10 and 11 is made of a material 12 having high bending rigidity. For example, when the member to be bonded is FRP, it is possible to locally change the manufacturing method (the material of the glass fiber, the weaving method, the forming method, and the like) between the vicinity of the bonding portion and other portions to locally manufacture a material having a large bending rigidity. it can.

The plate thickness is increased only at the bonding portion. As shown in FIG. 15, only the bonding portion of the two members 13 and 14 is made thicker. For example, when the member to be bonded is a metal, a material having a large thickness can be manufactured by machining, and in the case of an FRP, a material having a large thickness can be partially manufactured by increasing the number of layers.

The lap adhesive joint described above can be used to bond an automobile body skeleton member or a panel flange with an adhesive portion and a weld bonding joint portion, or to connect a railroad vehicle side structure assembling portion and a side groove to a roof or a bogie. Applicable to departments.

[0026]

Since the present invention is constructed as described above, in addition to the effect that the adhesive strength can be improved, no special processing such as tapering is required, and the adhesive is applied from the end. There is no aging deterioration of the strength seen in the protruding method, and an effect that an adhesive having desired characteristics can be used without particularly selecting an adhesive having a low elastic modulus can be expected. Furthermore, when the same adhesive strength is sufficient, the wrap length of the adhesive joint can be shortened, so that the following effects can be obtained. In the case where the joint portion comes to a position where it interferes with another member in the device design, shortening the wrap length makes it possible to ease the design constraint concerning the engagement with the other member. Also, the shorter the wrap length, the smaller the required amount of adhesive, and the lower the cost. Further, as the wrap length is shorter, the work time for cleaning the adhesive surface, applying the adhesive, and the like is reduced, and the productivity can be improved by reducing the number of bonding steps.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the destruction of an adhesive portion of a lap adhesive joint.

FIG. 2A is a side view of a lap adhesive joint having a tapered portion, and FIG. 2B is a side view of a simple lap adhesive joint.

FIG. 3 is a view showing the adhesive strength of the adhesive joint of FIG. 2 (a).

FIG. 4 is a perspective view of a lap adhesive joint with an adhesive protruding from an end.

FIG. 5 is a diagram showing a change in shear stress of an adhesion portion in a lap adhesive joint depending on the thickness of an adherend.

FIG. 6 is a diagram showing a change in shear stress of an adhesive portion due to a difference in a material (Young's modulus) of an adherend in a lap adhesive joint.

FIG. 7 is a diagram showing the effect of the thickness of the adherend on the adhesive strength of the lap adhesive joint.

FIG. 8 is a diagram showing the influence of the Young's modulus of the adherend on the adhesive strength of the lap adhesive joint.

FIG. 9 is a diagram showing the effect of the bending rigidity of the adherend on the adhesive strength of the lap adhesive joint.

FIG. 10 is a view showing a state in which a contact plate is adhered to the vicinity of an adhesion portion of an adherend in a lap adhesive joint.

FIG. 11 is a diagram showing a change in shear stress of a bonded portion in a case where an abutment plate is bonded near a bonded portion of an adherend in a lap adhesive joint, and in a case where a bonded plate is not bonded.

FIG. 12 is a diagram showing the effect of the length of the plate on the adhesive strength of the lap adhesive joint.

FIG. 13 is a diagram showing the influence of the bonding position of the plate on the bonding strength in the lap bonding joint.

FIG. 14 is a view showing a case where a material having high bending rigidity is used only in the bonding portion in order to increase the bending rigidity of the bonding portion in the lap adhesive joint.

FIG. 15 is a diagram showing a case where only the bonding portion of the adherend is made thicker in order to increase the bending rigidity of the bonding portion in the lap adhesive joint.

[Explanation of symbols]

 1a, 1b ... adherend 2 ... adhesive layer 3 ... taper 7, 8, 10, 11, 13, 14 ... member 9, S ... this plate

Claims (2)

[Claims] 1. A lap adhesive joint in which two members are overlapped and bonded, wherein the bending rigidity of the two members to be bonded is locally increased only in the vicinity of the bonded portion. 2. The lap adhesive joint according to claim 1, wherein the means for locally increasing the bending stiffness in the vicinity of the adhesive portion is a contact plate.